Database Management Entity – Relationship (ER) Diagram

Prof. Sridhar Vaithianathan

DATA MODELING

A Data Model is a map or diagram that represents entities and their relationships.

Some Definitions

A File/Entity/Table: A group or collection of similar records

A record / Tuple: one piece of data, i.e., one student's information, a recipe, a test question.

Records = rows A field/Attributes: one category of information,

i.e., Name, Address, Semester Grade, Academic topic

(Fields = columns)

ER Diagram - Example

CARDINALITY AND MODALITY

Entity Relationship Diagram - Notation

Entitiy

Relationship

Associated Object

Mandatory (Exactly) One

Optional (Zero or one) One

Mandatory Many

Optional Many

Optional

Mandatory

E – R Diagram Example

Basket Ball Game

Entities:

Home Stadium

Team

Player

Games

ER – Diagram Example – Basket Ball Game

HOME STADIUM TEAM

PLAYER

Has

Has

GAME

Participates

Has

Entities, Attributes and Relationship Strong Entity Vs Weak entity ( EMPLOYEE &

DEPENDENT) Simple Vs Composite Attributes Single Valued Vs Multi Valued Attributes Stored Vs Derived Attributes Identifier Attribute – Primary Key Composite Identifier Foreign Key Sub-Type Vs Super Type Relationship

Database Associations ExampleHOME STADIUM

Stadium Id Stadium Name, Capacity, Location

TEAM

Team Id Team Name

PLAYER

Player Id Player Name, Position

GAME

Team id(1) Team id(2) Date Final Score

BASKET BALL GAME

Relationship Example Instructions

One-to-One.

TEAMTeam Id Team Name, Stadium Id

Each team has only one home stadium, and each home stadium has only one team.

STADIUM and TEAM

Place the primary key from one entity to other entity as a foreign key and vice versa.(i.e. foreign key can be placed at either side of the relationship.)

One-to-Many

PLAYERPlayer Id Player Name, Position, Team Id

Each player is on only one team, but each team has many players.

PLAYER and TEAM

Place the primary key from the entity on the one side of the relationship as a foreign key in the table for the entity on the many side of the relationship

Many-to-Many

PLAYER STATISTICS

Team id(1), Team id(2), Date, Player Id Points

Each player participates in many games and each game has many players.

PLAYER and GAME

Create a third entity/table and place the primary keys from each of the original entities together in the third table as a combination primary key

DATABASE ASSOCIATIONS …

ER – Diagram : Basket Ball Game

HOME STADIUM TEAM

GAME STATISTICS

PLAYER

GAME

Has

Partici-pates Has

Has

Has

ERD Development Process

Identify the entities Determine the attributes for each entity Select the primary key for each entity Establish the relationships between the

entities Draw an entity model Test the relationships and the keys

THANKS

THANKS

THANKS

THANKS

THANKS